Over 50 years since discovery of a ferroelectric barium titanium oxide BaTi2O5, researches on ferroelectrics with a focus on applications thereof have been carried out energetically around the world.
A ferroelectric material having a high permittivity, a piezoelectric property, a pyroelectric property, an electrooptic effect and a nonlinear optical effect is applied to various fields, such as electrical and optical fields, and used as a capacitor, an amplifying element, a piezoelectric resonant element, a pyroelectric element, a light modulator and a wavelength conversion element. In particular, recent years, great interest has been shown in researches and applications of a transparent ferroelectric oxide glass. The ferroelectric glass can be crystallized to control its optical properties, and therefore expected to be utilized as a high-performance light modulator (electrical signal/light signal conversion), optical switch (change in direction of a light path) and wavelength conversion element (change in wavelength of a laser beam). Further, the ferroelectric glass is suited to mass production at low cost in view of advantageous capability to be produced through short processes. Thus, the research and development of the ferroelectric glass are highly significant from an industrial perspective as well as scientific and engineering perspectives.
While the ferroelectric BaTi2O5 has excellent dielectric characteristics, it is extremely difficult to be formed as bulk glass due to relatively high nucleation frequency and crystal growth rate in its solidification process. In previous reports, only a thin film-shaped glass was obtained even in a roll quenching method at a cooling rate of about 107 to 8 K/s (see the following Non-Patent Publication 1). Further, an addition of a glass forming element is required to obtain a ferroelectric glass (see the following Non-Patent Publication 2).                [Patent Publication 1] Japanese Patent Application No. 2003-284855        [Patent Publication 2] Japanese Patent Application No. 2004-020798        [Non-Patent Publication 1] K. Yoshimaru, Y. Ueda, K. Morinaga, T. Yanagase, Journal of the Ceramic Society of Japan, 1984, 92: p 481        [Non-Patent Publication 2] A. Narasaki, K. Tanaka, K. Hirao, Appl. Phys. Lett. 1999; 75: p 3399        